Method and Apparatus for Back End of Line Semiconductor Device Processing

ABSTRACT

A via opening including an etch stop layer (ESL) opening and methods of forming the same are provided which can be used in the back end of line (BEOL) process of IC fabrication. A metal feature is provided with a first part within a dielectric layer and with a top surface. An ESL is formed with a bottom surface of the ESL above and in contact with the dielectric layer, and a top surface of the ESL above the bottom surface of the ESL. An opening at the ESL is formed exposing the top surface of the metal feature; wherein the opening at the ESL has a bottom edge of the opening above the bottom surface of the ESL, a first sidewall of the opening at a first side of the metal feature, and a second sidewall of the opening at a second side of the metal feature.

This application is a divisional application of U.S. patent Ser. No.13/891,578, filed May 10, 2013, entitled “Method and Apparatus for BackEnd of Line Semiconductor Device Processing,” which claims priority toU.S. Provisional Application Ser. No. 61/777,219, filed Mar. 12, 2013,which applications are incorporated herein by reference in its entirety.

BACKGROUND

Generally, integrated circuits (ICs) comprise individual devices, suchas transistors, capacitors, or the like, formed on a substrate. One ormore metal layers are then formed over the individual devices to provideconnections between the individual devices and to provide connections toexternal devices. The front-end-of-line (FEOL) is the first portion ofIC fabrication where the individual devices (transistors, capacitors,resistors, etc.) are patterned in a wafer. FEOL generally coverseverything up to (but not including) the deposition of metal layers. Theback end of line (BEOL) is the second portion of IC fabrication wherethe individual devices get interconnected with wiring or metal layers onthe wafer. BEOL generally begins when the first metal layer is depositedon the wafer. It includes contacts, insulating layers, metal layers, andbonding sites for chip-to-package connections.

The metal layers interconnecting individual devices typically comprisean inter-metal dielectric (IMD) layer in which interconnect structures,such as vias and conductive lines, are formed, through numerous andrepetitive steps of deposition, patterning and etching of thin films onthe surface of silicon wafer. Interconnections between different metallayers are made by vias, which go through insulating IMD layersseparating metal layers and allow for communications between devicesformed at metal layers to communicate with other devices in the metallayers or directly with the semiconductor devices in the substrate.

The IMD layers may be etched to create via openings, via holes, ortrenches for conduction lines for metal layers. The etch processgenerally has certain over etch or under etch amount around the viaopenings, via holes, or trenches, due to overall process variation. Itis possible that a via opening is over etched so that a via does notfully land on the under-layer metal, causing via to under-layerdielectric recess. It is also possible a via opening is not etchedenough, causing via depth loading. Furthermore, a misplaced via may berisky for via to under-layer metal bridge causing circuit failure. Newmethods and apparatus are needed to avoid via to under-layer dielectricrecess, via depth loading, and via to under-layer metal bridge issues.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates in a cross sectional view various metal layers formedon individual devices of an integrated circuit (IC) in accordance withsome embodiment;

FIGS. 2(a)-2(g) illustrate in cross sectional views an etch stop layer(ESL) opening exposing a metal feature in a metal layer, in accordancewith some embodiments; and

FIGS. 3(a)-3(k) illustrate in cross sectional views a process of makingan etch stop layer (ESL) opening exposing a metal feature in a metallayer, in accordance with some embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that theembodiments of the present disclosure provide many applicable conceptsthat can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed are merely illustrative of specific waysto make and use the disclosure, and do not limit the scope of thedisclosure.

A via opening comprising an etch stop layer (ESL) opening and methods offorming the same are provided in accordance with various exemplaryembodiments, which can be used in the back end of line (BEOL) process ofIC fabrication. A metal feature is provided with a first part within adielectric layer and with a top surface. An ESL is formed with a bottomsurface of the ESL above and in contact with the dielectric layer, and atop surface of the ESL above the bottom surface of the ESL. An openingat the ESL is formed exposing the top surface of the metal feature;wherein the opening at the ESL has a bottom edge of the opening abovethe bottom surface of the ESL, a first sidewall of the opening at afirst side of the metal feature, and a second sidewall of the opening ata second side of the metal feature. The ESL opening exposing the metalfeature is separated from any other metal features within the samedielectric layer. The ESL opening around the metal feature whileexposing the top surface of the metal feature can make via formed withinthe ESL opening to be connected to the metal feature without via tounder-layer dielectric recess, via depth loading, and via to under-layermetal bridge issues.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, or connected or coupled to the other element orlayer or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to” or “directly coupled to” another element or layer, thereare no intervening elements or layers present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present inventive concept.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “above” or “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,”—when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. It shouldbe appreciated that the following figures are not drawn to scale;rather, these figures are merely intended for illustration.

FIG. 1 illustrates in a cross sectional view various metal layers formedon individual devices of an integrated circuit (IC) in accordance withsome embodiment. An illustrative IC is shown in FIG. 1 comprisingindividual devices, such as transistors, capacitors, or the like, formedon a substrate 900. Multiple metal layers 910, 920, 930, 940, and 950are then formed over the individual devices to provide connections amongthe individual devices and to provide connections to external devices.On top of the substrate layer 900 is a layer 901 which is the firstinter-layer dielectric (ILD) between a first metal layer 910 and thesubstrate layer 900. On top of the ILD layer 901 is the first metallayer 910, where a plurality of metal contacts are located and connectedto the devices within the substrate layer 900 by vias through the ILDlayer 901. The first metal layer 910 may be called the metal layer M₁. Asecond metal layer 920, which may be called the metal layer M₂, islocated on top of the first metal layer 910 separated by an inter-metaldielectric (IMD) layer 902. Similarly, additional metal layers 930, 940,and 950 are formed on top of each other and separated by IMD layers 903,904, and 905, respectively. Metal contacts between different metallayers are connected by vias such as via 911, 921, 931, and 941,respectively. The number of metal layers 910 to 950 and the number ofvias 911-941 connecting the metal layers are only for illustrativepurposes and are not limiting. There could be other number of layersthat is more or less than the five metal layers shown in FIG. 1.

The substrate layer 900 may comprise, for example, bulk silicon, dopedor undoped, or an active layer of a semiconductor-on-insulator (SOI)substrate. Generally, an SOI substrate comprises a layer of asemiconductor material, such as silicon, formed on an insulator layer.The insulator layer may be, for example, a buried oxide (BOX) layer or asilicon oxide layer. The insulator layer is provided on a substrate,typically a silicon or glass substrate. Other substrates, such as amulti-layered or gradient substrate may also be used.

The substrate 900 may comprise electrical devices such as various n-typemetal-oxide semiconductor (NMOS) and/or p-type metal-oxide semiconductor(PMOS) devices, such as transistors, capacitors, resistors, diodes,photo-diodes, fuses, and the like, interconnected to perform one or morefunctions. The functions may include memory structures, processingstructures, sensors, amplifiers, power distribution, input/outputcircuitry, or the like.

Shallow trench isolations (STIs), or other isolation structures, may beformed in substrate 900 to isolate device regions. STIs may be formed byetching substrate 900 using photolithography techniques to formrecesses. Generally, photolithography involves depositing a photoresistmaterial, which is then masked, exposed, and developed. After thephotoresist mask is patterned, an etching process may be performed toremove unwanted portions of the substrate 900. In an embodiment in whichthe substrate comprises bulk silicon, the etching process may be a wetor dry, anisotropic or isotropic, etching process. The recesses are thenfilled with a dielectric material such as an oxide layer formed by anyoxidation process, such as wet or dry thermal oxidation in an ambientcomprising an oxide, H₂O, NO, or a combination thereof, or by chemicalvapor deposition (CVD) techniques using tetra-ethyl-ortho-silicate(TEOS) and oxygen as a precursor. A planarization step may be performedto planarize the surface of the isolation material with a top surface ofthe substrate 900. The planarization step may be accomplished, forexample, using a chemical mechanical polishing (CMP) process known andused in the art.

A first insulating layer 901, e.g., an inter-layer dielectric (ILD)layer, is formed over the substrate 900. The ILD layer 901 may comprisea low dielectric constant (k value less than about 3.0) or an extremelow dielectric constant (k value less than about 2.5) material. Forexample, the ILD layer 901 may comprise an oxide, silicon dioxide(SiO₂), borophosphosilicate glass (BPSG), TEOS, spin-on glass (SOG),undoped silicate glass (USG), fluorinated silicate glass (FSG),high-density plasma (HDP) oxide, or plasma-enhanced TEOS (PETEOS). Aplanarization process, such as a CMP process, may be performed toplanarize the ILD layer 901.

The process forming the individual devices such as transistors,capacitors, resistors, diodes, photo-diodes, fuses, STIs, and the like,within the substrate 900 and the ILD layer 901 may be collectivelyreferred as the front-end-of-line (FEOL) process, which is the firstportion of IC fabrication where the individual devices (transistors,capacitors, resistors, etc.) are patterned in a wafer. FEOL generallycovers everything up to (but not including) the deposition of metallayers.

Following the FEOL process is the back end of line (BEOL) process, whichis the second portion of IC fabrication where the individual devices areinterconnected with wiring or metal layers 910 to 950 on the IC as shownin FIG. 1. The BEOL process generally begins when the first metal layer910 or M₁ is deposited on the wafer. It includes contacts, insulatinglayers, metal layers, and bonding sites for chip-to-package connections.As the result, the metal layers 910 to 950 as illustrated in FIG. 1, orone or more metal layers M₁-M_(n) in general, may be formed over the ILDlayer 901. A typical IC may comprise three or more metal layers,followed by a final passivation layer, not shown in FIG. 1. The finalpassivation layer may be used for protecting the IC from mechanicalabrasion during probe and packaging and to provide a barrier tocontaminants. After the final passivation layer, the bond pads forinput/output will be opened, followed by the normal post-fabricationprocess such as wafer probe, die separation, and packaging.

In more details, the BEOL process may comprise a sequence of steps:adding a metal layer M₁, adding an intra-metal dielectric (IMD) layer,making vias through the IMD layer to connect to lower metal layercontacts, and forming higher metal layer contacts connected to the vias,or creating vias and conductive lines of a higher metal layer by etchingvia holes and trenches for the conductive lines at the same time. Themetal layers 910 to 950 shown in FIG. 1 are separated by IMD layers 902to 905. The IMD layers 902 to 905 may comprise multiple sub-layers. TheIMD layers 902 to 905 may comprise a dielectric layer and an etchingstop layer (ESL). A dielectric layer may comprise a low dielectricconstant or an extreme low dielectric constant (ELK) material. Aplanarization process, such as a chemical-mechanical polish (CMP)process, may be performed to planarize the various IMD layers.

The metal layers 910 to 950 as illustrated in FIG. 1, or one or moremetal layers M₁-M_(n) in general, may be formed of any suitableconductive material, such as a highly-conductive metal, low-resistivemetal, elemental metal, transition metal, or the like. In an embodimentthe metal layers M₁-M_(n) may be formed of copper (Cu), although othermaterials, such as tungsten (W), aluminum (Al), gold (Au), or the like,could alternatively be utilized. Copper (Cu) has a more desirablethermal conductivity and is available in a highly pure state. In anembodiment in which the metal layers M₁-M_(n) are formed of copper (Cu),the metal layers M₁-M_(n) may be deposited by electroplating techniques,although any method of formation could alternatively be used.

The metal layers 910 to 950 as illustrated in FIG. 1, or one or moremetal layers M₁-M_(n) in general, may be formed, using a plating andetching process through a damascene or dual-damascene process, in whichopenings are etched into the corresponding dielectric layer and theopenings are filled with a conductive material such as Cu. The damasceneprocess means formation of a patterned layer imbedded on and in anotherlayer such that the top surfaces of the two layers are coplanar. An IMDis deposited either directly on a substrate, or on top of anotherexisting metal layer. Once the IMD is deposited, portions of the IMD maybe etched away to form recessed features, such as trenches and vias,which can connect different regions of the IC and accommodate theconductive lines. A damascene process which creates either only trenchesor vias is known as a single damascene process. A damascene processwhich creates both trenches and vias at once is known as a dualdamascene process. Damascene and dual-damascene processes use lowerresistance metals such as copper (Cu) to form many metal elements (e.g.lines, interconnects, and the like) instead of the conventionally usedaluminum (Al).

Interconnections between different metal layers are made by vias, suchas the vias 911, 921, 931, and 941 as shown in FIG. 1. A via goesthrough an insulating IMD layer separating two metal layers, andconnects to another metal feature to allow for communication betweeninterconnects of other metal layers or directly with the semiconductordevices in the substrate. An IMD layer 902, 903, 904, or 905 may beetched to create a via opening, a via hole, or a trench for a conductionline. The etch process generally has certain over etch or under etchamount around the via opening, the via hole, or the trench, due tooverall process variation. It is possible that a via opening is overetched so that a via does not fully land on the under-layer metal,causing via to under-layer dielectric recess. It is also possible a viaopening is not etched enough, causing via depth loading. Furthermore, amisplaced via may be risky for via to under-layer metal bridge causingcircuit failure. More details of an IMD layer, a via opening, a via, andthe connection between a via and other metal feature are shown in FIGS.2(a)-2(g), and FIGS. 3(a)-3(g), which can prevent the problems statedabove.

FIGS. 2(a)-2(g) illustrate in cross sectional views an IMD layer 907comprising a plurality of dielectric layers 109 and 105, and a pluralityof etch stop layers (ESLs) 103 and 107. The IMD layer 907 may be any ofthe IMD layers 902-905 shown in FIG. 1. The dielectric layers 105 and109, and the ESLs 103 and 107 are the sub-layers of the IMD layer 907.There may be multiple dielectric layers such as the dielectric layer 105and 109 for the IMD layer 907. In between two dielectric layers 105 and109 may be an ESL 107. The dielectric layer 109 and the ESL layer 107are optional. The IMD layer 907 may have a dielectric layer 105 and anESL 103 only without the layers 107 and 109. There may be otherdielectric layer formed above the ESL 103, which is shown in FIGS.3(i)-3(k). A metal feature 101 is contained within the IMD layer 907.The IMD layer 907 may contain additional metal features such as themetal feature 111. As illustrated in FIGS. 2(a)-2(g), the metal feature101 goes through the dielectric layers 105 and 109.

The dielectric layer 105 and 109 may comprise a material, such as anoxide, silicon dioxide (SiO₂), borophosphosilicate glass (BPSG),tetra-ethyl-ortho-silicate (TEOS), spin-on glass (SOG), undoped silicateglass (USG), fluorinated silicate glass (FSG), high-density plasma (HDP)oxide, or plasma-enhanced TEOS (PETEOS). The dielectric layers 105 and109 may comprise a SiOC-based spin-on material that can be applied to ordeposited by a spin-on method, such as spin coating. The dielectriclayers 105 and 109 may each have a thickness of from about 300 Å toabout 1200 Å.

The ESL 107 may be formed in between two dielectric layers 105 and 109.The etching stop layer (ESL) 103 may be formed above the dielectriclayer 105. The ESL 103 has a bottom surface 214 above and in contactwith the dielectric layer 105, and a top surface 212 of the ESL 103 isabove the bottom surface 214 of the ESL 103. The ESLs 103 and 107protect any underlying layer or layers during the etching process.Materials for the ESLs 103 and 107 may include SiC, SiCN, SiOC, AlN,SIN, TEOS, or hard black diamond (HBD), or the like. Alternatively, theESL 103 may be formed by depositing and annealing a metal oxidematerial, which may include hafnium (Hf), hafnium oxide (HfO2), oraluminum (Al). The material used for the ESLs 103 and 107 may depend onthe materials used for the dielectric layers 109 and 105, in addition tothe dielectric layer above the ESL 103. The selection of the materialfor the ESLs 103 and 107 may be based on the desired etch ratedifference between the etch rate for the ESLs 103 and 107 and the etchrate for the dielectric layers 109 and 105 and the dielectric layerabove the ESL 103. For example, the selection of the material may makethe etch rate of the ESLs 103 and 107 to be 90% slower than the etchrate of the dielectric layers. Alternatively, the etching rate for thedielectric layers 109 and 105 may be at a rate about 640 Å/min, whilethe etching rate for the ESLs 103 and 107 may be at a range from about170 Å/min to about 440 Å/min.

Those layers 103, 105, 107, and 109 may be deposited by methodsincluding chemical vapor deposition (CVD), plasma enhanced chemicalvapor deposition (PECVD), high density plasma chemical vapor deposition(HDP-CVD) and atmospheric pressure chemical vapor deposition (APCVD).

FIGS. 2(a)-2(g) illustrate a metal feature 101 within the IMD layer 907.The metal feature 101 may be a via or a conductive line in a lower metallayer, which may be any of the metal layers 910 to 940 shown in FIG. 1.A second metal feature 111 may be formed separated from the metalfeature 101. The metal features 101 and 111 may be formed of anysuitable conductive material, such as a highly-conductive metal,low-resistive metal, elemental metal, transition metal, or the like. Inan embodiment the metal features 101 and 111 may be formed of copper(Cu), although other materials, such as tungsten (W), aluminum (Al),gold (Au), or the like, could alternatively be utilized.

FIGS. 2(a)-2(g) illustrate an ESL opening 202 of the ESL 103 whichexposes a top surface 102 of the metal feature 101. The ESL opening 202may be a part of a via opening shown in FIG. 3(j), where the via openingfurther comprises an opening 302 at a dielectric layer 301 above the ESL103. The ESL opening 202 around the metal feature 101 while exposing thetop surface 102 of the metal feature 101 can make via formed within theESL opening 202 to be connected to the metal feature 101 without via tounder-layer dielectric recess, via depth loading, and via to under-layermetal bridge issues. As later shown in FIG. 3(k), a via 303 and a metalline 305 may be connected to the metal feature 101 filling the ESLopening 202 shown in FIGS. 2(a)-2(g).

The metal feature 101 has a top surface 102. As shown in FIGS. 2(a),2(c), and 2(d), the top surface 102 of the metal feature 101 is abovethe dielectric layer 105, while a part of the metal feature 101 may bewithin the dielectric layer 105. The height of the top surface 102 ofthe metal feature 101 above the dielectric layer 105 may be in a rangefrom about 50 Å to about 150 Å. Alternatively, as shown in FIG. 2(b),the top surface 102 of the metal feature 101 may be substantiallyhorizontally aligned with the surface of the dielectric layer 105 whenthe metal feature 101 is all within the dielectric layers 105 and 109.Similarly, the top surface 102 of the metal feature 101 may be below thetop surface 212 of the ESL 103, as shown in FIGS. 2(a)-2(c).Alternatively, the top surface 102 of the metal feature 101 may besubstantially horizontally aligned with the top surface 212 of the ESL103, as shown in FIG. 2(d).

The opening 202 of the ESL 103 may be formed to expose the top surface102 of the metal feature 101. The depth of the opening 202 may be in arange from about 50 Å to about 150 Å. The opening 202 at the ESL 103exposing the top surface 102 of the metal feature 101 may not expose thesecond metal feature 111. The opening 202 has a bottom edge 204 which isabove the bottom surface 214 of the ESL 103. The opening 202 has a firstsidewall 208 at a first side of the metal feature 101, and a secondsidewall 209 of the opening 202 at a second side of the metal feature101. The bottom edge 204 of the opening 202 at the ESL may be lower thanthe top surface 102 of the metal feature 101, as shown in FIGS. 2(a) and2(d). Alternatively, the bottom edge 204 of the opening 202 at the ESL103 may be substantially horizontally aligned with the top surface 102of the metal feature 101, as shown in FIG. 2(c). Still alternatively,the bottom edge 204 of the opening 202 at the ESL may be above the topsurface 102 of the metal feature 101, as shown in FIG. 2(b).

The first sidewall 208 of the opening 202 may be substantially alignedto a first edge 211 of the metal feature 101, as shown in FIG. 2(e). Thesecond sidewall 209 of the opening 202 may be substantially aligned to asecond edge 213 of the metal feature 101, as shown in FIG. 2(e).Alternatively, there may be a gap between the first sidewall 208 and thesecond sidewall 209 of the opening 202 and an edge of the metal feature101, as shown in FIGS. 2(a) and 2(d). The opening 202 at the ESL 103 maybe of a rectangle shape, as shown in FIG. 2(a). Alternatively, theopening 202 at the ESL 103 may be of a circle, a square, an octagon, anoval, or a diamond, or any other irregular shape, as shown in FIG. 2(d).

Some additional embodiments are shown in FIGS. 2(f)-2(g), where the ESL103 may comprise two sub-layers 1031 and 1032. The ESL 103 comprises afirst sublayer 1031 made of a first material and a second sublayer 1032made of a second material. The first material may be a conventional ESLmaterial such as SiCN or SiOC, while the second material may be a newESL material such as AlN, and vice versa. Alternatively, the firstmaterial and the second material may be any different ESL materials. Theopening 202 at the ESL goes through the first sublayer 1031 andcomprises a part opening at the second sublayer 1032 to expose the topsurface 102 of the metal feature 101 as illustrated in FIG. 2(f).Alternatively, the opening 202 at the ESL comprises an opening at thefirst sublayer 1031 only to expose the top surface 102 of the metalfeature 101, as illustrated in FIG. 2(g).

FIGS. 3(a)-3(k) illustrate in cross sectional views a process of makingan etch stop layer (ESL) opening 202 exposing a top surface 102 of ametal feature 101, in accordance with some embodiments. The ESL opening202 may be a part of a via opening shown in FIG. 3(j), where the viaopening further comprises an opening 302 at a dielectric layer 301 abovethe ESL 103. The ESL opening 202 around the metal feature 101 whileexposing the top surface 102 of the metal feature 101 can make viaformed within the ESL opening 202 to be connected to the metal feature101 without via to under-layer dielectric recess, via depth loading, andvia to under-layer metal bridge issues. As shown in FIG. 3(k), a via 303and a metal line 305 may be connected to the metal feature 101 fillingthe ESL opening 202 shown in FIGS. 2(a)-2(g).

As illustrated in FIG. 3(a) in a cross sectional view, a part of an IMDlayer 907 may be provided. The part of the IMD layer 907 comprises aplurality of dielectric layers 109 and 105, and an ESL 107 between thedielectric layer 105 and 109. The dielectric layers 105 and 109, and theESL 107 are the sub-layers of the IMD layer 907. The dielectric layer109 and the ESL layer 107 are optional. The part of the IMD layer 907may have a dielectric layer 105 only without the layers 107 and 109.

A metal feature 101 is contained within the IMD layer 907. The IMD layer907 may contain additional metal features such as the metal feature 111.The metal feature 101 goes through the dielectric layers 105 and 109. Atop surface 102 of the metal feature 101 is substantially horizontallyaligned with the top of the dielectric layer 105.

As illustrated in FIGS. 3(b) and 3(d), an ESL 103 may be formed with abottom surface of the ESL above and in contact with the dielectric layer105, and a top surface 212 of the ESL above the bottom surface of theESL. The ESL 103 may be formed in various different ways. As illustratedin FIG. 3(b), the ESL 103 may be formed on the dielectric layer 105 asprovided in FIG. 3(a), where the top surface 102 of the metal feature101 is aligned with the surface of the dielectric layer 105.Alternatively, the dielectric layer 105 may be etched away so that thetop surface 102 of the metal feature 101 is above the dielectric layer105, as illustrated in FIG. 3(c). An ESL 103 can then be formed on thenew dielectric layer 105 as illustrated in FIG. 3(d). As illustrated inFIGS. 3(c)-3(d), the top surface 102 of the metal feature 101 is abovethe dielectric layer 105, while a part of the metal feature 101 may bewithin the dielectric layer 105. The height hl of the top surface 102 ofthe metal feature 101 above the dielectric layer 105 may be in a rangefrom about 50 Å to about 150 Å. Alternatively, as shown in FIG. 3(b),the top surface 102 of the metal feature 101 may be substantiallyhorizontally aligned with the surface of the dielectric layer 105 whenthe metal feature 101 is all within the dielectric layers 105 and 109.

The ESL 103 formed as shown in FIG. 3(b) or 3(d) can be furtherprocessed, as illustrated in FIGS. 3(e)-3(h). As illustrated in FIG.3(e), the top surface 212 of the ESL 103 may be further etched to bethinner than the first formed in FIG. 3(h), yet still fully cover thetop surface 102 of the metal feature 101. Alternatively, as illustratedin FIG. 3(f), the top surface 212 of the ESL 103 may be further etchedto be thinner and substantially horizontally aligned with the topsurface 102 of the metal feature 101. Alternatively, as illustrated inFIG. 3(g), the top surface 212 of the ESL 103 may be further etched tobe thinner but still higher than the top surface 102 of the metalfeature 101, yet there is an opening 202 above the top surface 102 ofthe metal feature 101. Still alternatively, as illustrated in FIG. 3(h),the top surface 212 of the ESL 103 may be further etched to form apattern with an opening 402 above the top surface 102 of the metalfeature 101, surrounded by two parts 401 and 403 which are higher thanthe other part of the top surface 212 of the ESL 103.

The processed ESL 103 shown in FIGS. 3(e)-3(h) may be covered by adielectric layer. FIG. 3(i) shows a dielectric layer 301 covering theESL 103 as shown in FIG. 3(e). The dielectric layer 301 may be similarlyformed to cover the ESL 103 shown in FIGS. 3(f)-3(h), which is notshown. The dielectric layer 301 may be deposited by methods includingchemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), high density plasma chemical vapor deposition(HDP-CVD) and atmospheric pressure chemical vapor deposition (APCVD).

As illustrated in FIG. 3(j), an opening 302 at the dielectric layer 301and an opening 202 of the ESL 103 may be formed to expose the topsurface 102 of the metal feature 101. The depth of the opening 302 maybe in a range from about 500 Å to 1500 Å. The depth of the opening 202may be in a range from about 50 Å to about 150 Å. The opening 302 at thedielectric layer 301 goes through the dielectric layer 301. The opening202 at the ESL 103 exposes the top surface 102 of the metal feature 101while keep any other metal feature such as the metal feature 111 stillcovered by the ESL 103. The opening 202 has a bottom edge 204 which isabove the bottom surface of the ESL 103, and a top edge 206. The opening202 has a first sidewall 208 at a first side of the metal feature 101,and a second sidewall 209 of the opening 202 at a second side of themetal feature 101.

As shown in FIG. 3(j), the bottom edge 204 of the opening 202 at the ESL103 may be lower than the top surface 102 of the metal feature 101.There may be a gap between the first sidewall 208 of the opening 202 andan edge of the metal feature 101. There may be a gap between the secondsidewall 209 of the opening 202 and an edge of the metal feature 101 aswell. The opening 202 at the ESL 103 may be of a rectangle shape.

Alternatively, the bottom edge 204 of the opening 202 at the ESL 103 maybe substantially horizontally aligned with the top surface 102 of themetal feature 101, as shown in FIG. 2(c). Still alternatively, thebottom edge 204 of the opening 202 at the ESL may be above the topsurface 102 of the metal feature 101, as shown in FIG. 2(b). The firstsidewall 208 of the opening 202 may be substantially aligned to a firstedge 211 of the metal feature 101, as shown in FIG. 2(e). The opening202 at the ESL 103 may be of a circle, a square, an octagon, an oval, ora diamond, or any other irregular shape, as shown in FIG. 2(d). Allthose alternatives are not shown in the process demonstrated by FIGS.3(a)-3(k).

As illustrated in FIG. 3(k), a via 303 may be formed within the opening302 and 202 shown in FIG. 3(j). Furthermore, a conductive line 305 maybe formed above and connected to the via 303. The via 303 may be formedof a conductive material. The conductive material may be formed by anelectro-chemical plating process, CVD, ALD, PVD, a combination thereof,and/or the like. A planarization process, such as a chemical mechanicalpolishing (CMP) process, may be used to planarize and/or remove excessmaterial. Before forming the via 303, a liner layer, not shown, may beformed over the openings 302 and 202, covering the sidewalls and bottomof the openings 302 and 202. A thin barrier layer may be formed over theliner, if present, or may be deposited covering the sidewalls and abottom of the openings 302 and 202.

One of the broader forms of the present disclosure involves a device.The device comprises a metal feature having a first part within adielectric layer and having a top surface of the metal feature. Thedevice comprises an etching stop layer (ESL) with a bottom surface ofthe ESL above and in contact with the dielectric layer, and a topsurface of the ESL above the bottom surface of the ESL. An opening atthe ESL exposes the top surface of the metal feature. The opening at theESL has a bottom edge of the opening above the bottom surface of theESL, a first sidewall of the opening at a first side of the metalfeature, and a second sidewall of the opening at a second side of themetal feature.

Another of the broader forms of the present disclosure involves a methodof fabricating an integrated circuit (IC). The method comprises:providing a first dielectric layer; forming a metal feature, wherein themetal feature has a first part within the first dielectric layer and hasa top surface of the metal feature; forming an etching stop layer (ESL)with a bottom surface of the ESL above and in contact with the firstdielectric layer, and a top surface of the ESL above the bottom surfaceof the ESL; forming a second dielectric layer above and in contact withthe ESL; forming an opening through the second dielectric layer, andfurther forming an opening at the ESL exposing the top surface of themetal feature; wherein the opening at the ESL has a bottom edge abovethe bottom surface of the ESL, a first sidewall of the opening at theESL at a first side of the metal feature, and a second sidewall of theopening at the ESL at a second side of the metal feature.

Still another of the broader forms of the present disclosure involves adevice. The device comprises a first metal feature having a first partwithin a dielectric layer and having a top surface of the first metalfeature. The device comprises a second metal feature having a secondpart within the dielectric layer and separated from the first metalfeature. The device further comprises an etching stop layer (ESL) with abottom surface of the ESL above and in contact with the dielectriclayer, and a top surface of the ESL above the bottom surface of the ESL.An opening at the ESL exposes the top surface of the first metal featureand does not expose the second metal feature; wherein the opening at theESL has a bottom edge of the opening above the bottom surface of theESL, a first sidewall of the opening at a first side of the first metalfeature, and a second sidewall of the opening at a second side of thefirst metal feature.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps. In addition, eachclaim constitutes a separate embodiment, and the combination of variousclaims and embodiments are within the scope of the disclosure.

What is claimed is:
 1. A method of fabricating an integrated circuit (IC), the method comprising: forming a first dielectric layer; forming a first metal feature in the first dielectric layer, the first metal feature extending above an upper surface of the first dielectric layer; forming an etching stop layer (ESL) over the first dielectric layer and the first metal feature; forming a second dielectric layer above the ESL; and forming a first opening through the second dielectric layer and into the ESL, the first opening exposing a top surface of the first metal feature, wherein the first opening in the ESL has a bottom edge above a bottom surface of the ESL, a first sidewall of the first opening in the ESL at a first side of the first metal feature, and a second sidewall of the first opening in the ESL at a second side of the first metal feature.
 2. The method of claim 1, further comprising: thinning the first dielectric layer to expose the top surface of the first metal feature; and thinning the ESL so that the top surface of the ESL is substantially parallel with the top surface of the first metal feature.
 3. The method of claim 2, wherein thinning the first dielectric layer comprises recessing an upper surface of the first dielectric layer below an upper surface of the first metal feature.
 4. The method of claim 1, further comprising: forming a conductive via in the first opening; and forming a metal contact over the conductive via, the metal contact extending over an upper surface of the second dielectric layer.
 5. The method of claim 4, wherein the conductive via extends along sidewalls of the first metal feature.
 6. The method claim 1, further comprising: forming a second metal feature through the first dielectric layer, the second metal feature being completely covered by the ESL.
 7. A method of fabricating an integrated circuit (IC), the method comprising: forming a first metal feature in a first dielectric layer, the first metal feature protruding through an upper surface of the first dielectric layer; forming an etch stop layer over the first metal feature, the etch stop layer extending over the first metal feature; forming a recess in the etch stop layer, the first metal feature protruding above a bottom surface of the recess; and forming a second metal feature in the recess.
 8. The method of claim 7, further comprising forming a third metal feature in the first dielectric layer, wherein the etch stop layer extends over the third metal feature.
 9. The method of claim 8, wherein the etch stop layer extends along sidewalls of the third metal feature.
 10. The method of claim 7, wherein forming the etch stop layer comprises forming a layer of of SiC, SiCN, SiOC, AlN, SIN, tetra-ethyl-ortho-silicate (TEOS), or hard black diamond (HBD).
 11. The method of claim 7, wherein the second metal feature extends along sidewalls of the first metal feature.
 12. The method of claim 7, wherein forming the etch stop layer comprises thinning the etch stop layer prior to forming the recess.
 13. The method of claim 7, further comprising, prior to forming the recess, forming a second dielectric layer over the etch stop layer, and wherein forming the recess comprises forming the recess through the second dielectric layer.
 14. The method of claim 13, further comprising forming a conductive line over the second dielectric layer, the conductive line electrically coupled to the second metal feature.
 15. A method of fabricating an integrated circuit (IC), the method comprising: forming a first dielectric layer; forming a first metal feature in the first dielectric layer; recessing the first dielectric layer, the first metal feature protruding above an upper surface of the first dielectric layer after recessing; forming an etch stop layer over the first dielectric layer, the etch stop layer covering the first metal feature; forming a recess in the etch stop layer, a depth of the recess being less than a thickness of the etch stop layer, the first metal feature extending above a bottom of the recess; and forming a second metal feature in the recess.
 16. The method of claim 15, wherein the second metal feature extends along sidewalls of the first metal feature.
 17. The method of claim 15, wherein the etch stop layer is interposed between the second metal feature and the first dielectric layer.
 18. The method of claim 15, further comprising: forming a third metal feature in the first dielectric layer, wherein the etch stop layer extends over the third metal feature; and forming a second dielectric layer over the etch stop layer, wherein the etch stop layer is interposed between the third metal feature and the second dielectric layer.
 19. The method of claim 18, wherein upper surfaces of the first metal feature and the third metal feature are level.
 20. The method of claim 15, wherein forming the etch stop layer comprises: forming a first sublayer of a first material; and forming a second sublayer over the first sublayer, the second sublayer comprising a second material, wherein the recess extends through the second sublayer and into the first sublayer. 